To unlock all the ships, go to the machine's Test Menu. Enter "Game Settings", change everything to 9 on "Shooter1 Coin/Credits" and "Shooter2 Coin/Credits". Also turn On "Free Play". Now exit that menu and go to "I/O Test". Hold the Test and Service button and repeatedly press the 2nd player's Start button. If done right, you should see the "Days of Operation" counter increasing. Set it to over 140. Exit that menu and reset the "Shooter1 Coin/Credits", "Shooter2 Coin/Credits" and "Free Play" if you wish. You can now exit the Test Menu altogether and reboot the machine. If done right, all the ships will be selectable.